Kitchen timer hardware

Kitchen timer

We're building a Kitchen timer! The project is heavily inspired by REST: Kitchen timer by mkdxdx [Hackaday.io].

Features

• ⏱️ Allows several timers to run in parallel
• ⚡ Is battery powered and power efficient
• 🔌 Charged by USB-C
• 💻 Programmable through the same USB port
• 🐍 Easter eggs

Hardware

• Atmega328P as microcontroller
• Rotary encoder for setting the time
• 16x16 LED matrix as display
• 32 kHz crystal for accurate timekeeping
• Passive buzzer for beeping

See the bill of material in the KiCAD project for the full details.

Mechanical components

Additionally, you will need the following mechanical components for the assembly:

Manufacturing / gerber files

If you want to build the PCB yourself, you can download the latest release of Gerber files from Github: https://github.com/emanuelen5/kitchen-timer/releases/latest

Enclosure

The .stl files are available in ./enclosure so you can 3D-print the enclosure yourself.

Software

You can flash the program directly using the ISP header on the board if you want (the same procedure as flashing the bootloader, below). But it's more convenient to add the bootloader so you don't have to open up the enclosure for each software update. Then you can instead program it over the USB-C connector.

For that, you need the bootloader firmware and programmer software which you can download from https://github.com/emanuelen5/kitchen-timer/releases/tag/bootloader-v1.2.0.

Bootloader

To flash the microcontroller with the bootloader, you need avrdude. Avrdude 7.3 can be downloaded from https://github.com/avrdudes/avrdude/releases/tag/v7.3. Make sure to add it to your PATH.

Connect your programmer of choice to the 6-pin in-system programmer (ISP) connector:

Then run the following command (replace <programmer> with your programmer of choice, like usbtiny):

# the bootloader.hex file needs to be in the current directory
avrdude -p atmega328p -c <programmer> -U flash:w:bootloader.hex:i \
  -U lfuse:w:0x62:m -U hfuse:w:0xD0:m -U efuse:w:0xFF:m

[!TIP] Use avrdude -c ? to see which programmers are available

This flashes the bootloader and sets the required fuses for the bootloader.

After that you can disconnect the programmer and assemble the device.

Programmer

Now that you have the bootloader on the device, you can use the USB-C cable for programming it by using the programmer application.

Dependencies

First you will need to install some packages that the programmer needs (files from https://github.com/emanuelen5/kitchen-timer/releases/tag/bootloader-v1.2.0).

pip install -r ./programmer/requirements.txt

You can now program the application onto the device through the bootloader!

Upload firmware

Download the latest revision of the firmware (if you want to build it yourself, see #Development below) from the releases https://github.com/emanuelen5/kitchen-timer/releases.

Connect the USB cable to the device, and then run

python3 ./programmer/programmer.py --hexfile firmware.hex

Development

Firmware

To build the firmware, you need pio which can be downloaded from https://pypi.org/project/platformio/ or installed using pip (the official Package Installer for Python)

To build any of the environments, use the pio command, like

# builds the main application and puts it in .pio/builds/application/firmware.hex
pio run -e application

Then use the programmer to upload the firmware to the device.

Background

Our kitchen timer is an iteration of mkdxdx project "REST: Kitchen timerREST: Kitchen timer". We wanted to keep the "dial" (rotate-to-set) concept and the 16x16 led matrix but do it with an ATmega328p and a custom PCB. In the end we scrapped the dial since the design became too complicated, and settled on a simpler design.

Motivation

Both Erasmus Cedernaes and Nicolas Perozzi belong to Stockholm Makerspace. On the same day, we messaged each other a link to mkdxdx​ project. We were very excited about building something that would be "practical" so we decided to team up and work on this together. Additionally, we share an interest in working with the AVR MCUs. This project is a nice blend of programming, electrical, mechanical, 3d printing, and design but, without feeling overwhelming.